With the increasing complexity of electronic systems in the future, there is an urgent demand for high-density, low-cost, low-power and high-speed semiconductor memories, such as “flash memory.” Flash memory may refer to rewritable memory chips that hold their content without power. An example of a flash memory used to address the need for high-density, low-cost, low-power and high-speed semiconductor memories is an electrical erasable and programmable read-only memory (EEPROM). However, EEPROMs have large write/erase/read times in comparison to other types of semiconductor memories.
Write/erase/read times in EEPROMs may be improved by using what are known as “quantum dots” or nanocrystals embedded between the control oxide and the tunnel oxide in the flash memory. A quantum dot may refer to a small nanoparticle that contains a few electrons. These embedded quantum dots act as a floating gate and may improve the erase/write/read speed. Further, these embedded quantum dots or nanocrystals may improve the non-volatile charge retention time due to the effects of Coulomb blockade, quantum confinement, and reduction of charge leakage from weak spots in the tunnel oxide. Other areas of improvement include device scaling, operating power and device life time.
There have been several methods used in embedding nanocrystals including aerosol deposition, direct chemical vapor deposition (CVD) growth, and precipitation methods that use ion implantation and the deposition of Si-rich oxide layers. In each of these methods, the nanocrystal size and position distribution cannot be controlled. By not being able to control the size and spatial distribution of the nanocrystals between the control oxide and the tunnel oxide, the device performance, scalability and manufacturability may be limited.
Therefore, there is a need in the art for a more uniform size and spatial distribution of the nanoparticles between the control oxide and the tunnel oxide.